added iosStoryboardExample

the new iosStoryboardExample demonstrates how ios storyboards can be
used with openframeworks.
Merge pull request #2803 from julapy/ios-storyboard-example

added iosStoryboardExample
setting the root application path inside ofxiOSAppDelegate was messy - cleaned up to one succinct line.
Merge pull request #2804 from julapy/ios-datapathroot-clean

cleaned up code for setting the root application path inside ofxiOSAppDelegate.